Also, I would like to thank M Simon, TallDave and their fellow bloggers for their continued interest in this technology. We appreciate that a great deal, but as you might imagine we have been a little too busy to communicate very much with the on-line people.
The difference between "square" vs "parabolic" is how hard the math is. For square, you have V=0 inside and V=big outside so particles only get accelerated near a boundary (and I assume it means they get accelerated into the center). For parabolic the potential is assumed to be uniformly changing as r^2, so particles gradually pick up more energy as they approach the center.
Both models are crude. Square is zeroth order crude, parabolic is first order crude. The assumption is that only one dimension is important - radial. The reality of the polywell is that it is 3D, the face of a coil is totally different than the cusp so the energy distribution is completely non-uniform in radius.
Lots of symmetry though, so a first order 3D calculation only needs to work on 1/48th of the volume. Until we do some 3D simulations, we really can't say anything about which chunk of physics will be important.
MSimon wrote:The next step is continuous operation. Following that (with the need for a few intermediate steps a possibility) Q=10.
Perhaps. There are some things I find about Bussard's talk to be troubling enough that I do wonder how much of the physics he really understood: For example, he claimed that p-11B fusion would be totally aneutronic. This is not so (0.1% of the reactions yield a neutron). A production machine will absolutely need shielding.
MSimon wrote:The next step is continuous operation. Following that (with the need for a few intermediate steps a possibility) Q=10.
Perhaps. There are some things I find about Bussard's talk to be troubling enough that I do wonder how much of the physics he really understood: For example, he claimed that p-11B fusion would be totally aneutronic. This is not so (0.1% of the reactions yield a neutron). A production machine will absolutely need shielding.
With the right fiddles (8 parts H to 1 part B11) it might be .01% That should give a shielding rqmt of 60% of a fission reactor.
If a fission reactor needs to sit 80 years to reduce long lived activation products to an acceptable level. A year or three should do the job for a pB11 machine.
Dr. Nebel thinks he understood the physics well enough.
Think about the inverse square law. If you need to be 100 ft from a neutronic machine for an acceptable radiation dose 3 feet should do for an aneutronic machine.
Consider that Dr. B had an hour and a half to teach 6 years of physics, 11 years of experimentation, and 100 years of geotechnical politics. Glossing over the radiation issue (since it is such a small and easily solvable problem) does not seem like a serious oversight.
Engineering is the art of making what you want from what you can get at a profit.
We should temper our optimism.... Dr. Bussard put IEC back on the map, but it is by no means guaranteed soon; Probability may be low to middle, but expected value is immense due to the potential payoff.... This has to be pursued.
On the downside, energy is misused as it is; We've got folks driving to work downtown and to the local office parks in huge SUVs and Pickup trucks; Fat 13 year old kids racing down local bike trails in ATVs, and Speedboats that runover folks engaged in more quiet or human centric activities.
If our optomism pans out with the polywell, I would favor dropping all taxes now levied on productive human behavior, no income tax, no capital gains tax, and transferring all revenue sources to come from energy. It'd be a joule tax, levied on energy from any source. It could free prouductive human behavior, and discourage some of the nonsense we seem to encourage by taxing the good stuff and letting the bad behavior go undiscouraged.
